1. Field of the Invention
The present invention relates to a high-frequency circuit device in a transmission/reception part of a high-frequency radio set, specifically, a mobile communication apparatus such as a mobile phone or the like. More specifically, this invention relates to a multiband high-frequency circuit device including a semiconductor amplifier circuit (hereinafter, referred to as a transmission amplifier circuit) for high-frequency power transmission and a switch circuit for switching among a plurality of communication systems and among a plurality of frequency bands.
2. Description of the Related Art
In a transmission amplifier circuit such as in a mobile phone or the like, high-frequency power is transmitted from an antenna according to a system in which a TDMA (Time Division Multiple Access) system used in Europe and a CDMA (Code Division Multiple Access) system coexist. In such a transmission amplifier circuit, separate high-frequency amplifiers are used so as to conform to the TDMA system and the CDMA system, respectively. This is based on the following reasons. That is, there is a difference in the respective output levels obtained according to these systems. Further, another difference is that: in the TDMA system, polar modulation or polar loop modulation is performed by, for example, an EDGE (Enhanced Data rates for GSM Evolution) modulation scheme; on the other hand, in the CDMA system, specifically, a W-CDMA (Wideband-Code Division Multiple Access) system or UMTS (Universal Mobile Telecommunication System), an operation is performed based on quadrature modulation, requiring a linear amplifier, and simultaneous transmission/reception also is performed. Thus, it has been the case that separate high-frequency amplifiers are assigned with respect to the TDMA system and the CDMA system, respectively.
FIG. 6 is a block diagram showing an example of the configuration of a conventional high-frequency circuit device. As shown in FIG. 6, a GSM (Global System for Mobile Communications)-based phase signal GSM PS Tx in the frequency band of 800 to 900 MHz according to the TDMA system is input to a high-frequency amplifier 3 of a transmission amplifier circuit and amplified. Further, a DCS (Digital Cellular System)-based or PCS (Personal Communication Services)-based phase signal DCS/PCS PS Tx in the frequency band of 1,700 to 1,900 MHz according to the CDMA system is input to a high-frequency amplifier 5 of the transmission amplifier circuit and amplified.
Meanwhile, in order to perform polar modulation, GSM and DCS/PCS amplitude signals are input from two power supply amplitude modulators 23 to power supply terminals of the high-frequency amplifiers 3 and 5, respectively. In this case, the high-frequency amplifiers 3 and 5 in the polar modulation operation can be realized by a high-frequency amplifier in saturation operation. Thus, current consumption can be reduced, so that even without using an isolator, it is very unlikely that the operation is disturbed due to the output impedance of the high-frequency amplifiers.
Meanwhile, in an operation according to the UMTS (W-CDMA) system, conventionally, a signal modulated by quadrature modulation is input to a high-frequency amplifier 2. In this case, unlike the high-frequency amplifiers 3 and 5 in polar modulation operation, it is required that the high-frequency amplifier 2 be a high-frequency amplifier in linear operation, and that an isolator 9 be provided on the output side of the high-frequency amplifier 2. A UMTS signal that has been modulated by quadrature modulation is input to the high-frequency amplifier 2 through a driver amplifier 17. The signal is supplied to an antenna 4 via a low-pass filter (LPF) 8, the isolator 9, a duplexer (shared device: DUP) 10, and GaAs switches 7. The duplexer (shared device) 10 is a filter for separating signals according to their frequency bands so as to perform transmission and reception simultaneously.
Furthermore, the isolator 9 is used to avoid the deterioration of a distortion characteristic in an operation of the high-frequency amplifier 2, which might result from an impedance deviating from 50 ohms when the antenna 4 is brought close to metal or a human head. The high-frequency amplifiers 2, 3 and 5 are formed of a FET or HBT (heterobipolar transistor) that is made from GaAs, a MOS FET made from Si, or a HBT made from SiGe.
The GaAs switches 7 are provided between the antenna 4 and each of the high-frequency amplifiers and between the antenna 4 and each reception circuit so as to switch between operations of GSM and DCS/PCS transmission and reception and to switch to an operation of UMTS simultaneous transmission/reception. The GaAs switches 7 may be formed of a pin diode. Further, in many cases, the LPFs 8 for suppressing harmonics from the high-frequency amplifiers 2, 3 and 5 are integrated into a switch module 6 with these switch circuits. Further, an entire high-frequency amplifier circuit also may be integrated into a module as a Tx module 20.
However, in such a configuration according to the conventional technique, compared with the case of a conventional mobile phone that is not conformable to a system in which the TDMA system and the CDMA system coexist but is specifically to either of the systems, a plurality of high-frequency amplifiers are required, resulting in a nearly 50% cost increase, and the isolator 9 is required with respect to the UMTS, resulting in another nearly 50% cost increase. That is, this configuration leads to almost doubling the cost, which has been disadvantageous. Further, since the isolator 9 is provided, an extra electric current of 40 to 70 mA is consumed in the high-frequency amplifier 2, which also is disadvantageous.